Blood samples are routinely taken in evacuated tubes, such as glass or plastic VACUTAINER.RTM. tubes (Becton Dickinson and Company) The patient end of a double ended needle is inserted into a patient's vein. The non-patient end of the same needle then punctures the septum of the stopper end of a blood collection tube. The elevated pressure of the patient's blood, relative to the evacuated tube, forces blood through the needle into the tube until the pressure in the tube equals the pressure in the patient's vein. Using this technique, a plurality of samples in separate tubes can be taken using a single needle puncture of the skin.
The exact volume of blood drawn by a device varies, depending upon ambient atmospheric conditions and the storage conditions of the tube up to the time of use. Industry standards specify a + or -10% allowable variation from the labeled draw volume at standard atmospheric conditions. Volumetric accuracy is required for precise control of analytical chemical reactions performed in the tube on freshly drawn samples. Shelf life ratings in excess of two years are acceptable for evacuated blood collection tubes.
To experimentally verify the shelf life of blood collection tubes in less than two years, an "Accelerated Aging" process is conventionally used. By elevating the storage temperature and pressure of the blood collection tubes, the aging process is accentuated. Based on calibration experiments or side by side comparison with control tube results, an estimate of the shelf life of a tube stored at room temperature and pressure can be made based on the results of measurement made under these accelerated aging conditions.
To make the shelf life measurement above, the required number of tubes (30 "test" tubes and 30 control tubes for example) are evacuated and placed in a pressurized cannister (typically 3 atm absolute) within an oven at elevated temperature (40.degree. C. for example). At specified time points, 5-10 days apart, a representative sample of the "test" tubes and control tubes, usually 5 of each, are removed from the chamber. Each individual tube is weighed before and after it is filled with water. The mass of water drawn into each tube is recorded by the operator.
The data from each time point are analyzed to make the shelf-life predictions. This Accelerated Aging Method is a destructive test consuming typically 60 tubes and requiring 45-90 days to complete. Due to variations in reading at each time point, the greater the shelf-life of a tube under test, the more time points are required to satisfactorily complete this measurement to a statistically significant result.
Therefore, there is a need in the art of blood collection for an expedient method, i.e., faster than 45-90 days, to evaluate the shelf life of evacuated blood collection tubes and, in particular, the shelf life of barrier coated thermoplastic blood collection tubes.